An LIRR retiree with a black belt in jiu jitsu got karate-chopped by the feds yesterday for allegedly scamming a lucrative disability pension.

Fred Catalano Jr., was among nine former railroad workers busted in a massive, $1 billion scheme to defraud the Railroad Retirement Board.

The roundup brought the total number of people charged in the “gravy train” case to 32, including former electrician Steven DeStefano, who quietly pleaded guilty last week and is cooperating with authorities.

According to a Manhattan federal court complaint, Catalano, 51, began seeing a doctor for his “purportedly disabling conditions” at around the same time he scored his fourth-degree black belt in March 2010.

Since retiring in May 2011 with a pension that paid him about $162,000 during the first 12 months, the former foreman has allegedly continued training for a fifth-degree black belt he plans to attain in 2015.

In addition, court papers say Catalano was “observed by law-enforcement agents attending jiu-jitsu and hot-yoga classes near his home on Long Island” within the last month.

Others arrested yesterday include former LIRR conductor James Maher, 59, who had 1,000-plus hours of OT in his final year at work despite claiming to suffer from pain that made it difficult to sit, stand, walk, bathe or dress himself.

Since retiring, Maher, who now lives in Florida, has allegedly worked on “strenuous home improvement projects” that included removing and reattaching a spiral staircase, and ripping up carpets.

He even brazenly told a neighbor he was “scamming the disability,” according to the Manhattan US Attorney’s Office.

Also busted were:

* Former LIRR transportation manager Michael Costanza, 59, who currently serves as chairman of the North Merrick, LI, Fire Department and who the feds say was injured fighting a fire five years after supposedly became disabled.

* Retired LIRR conductor Thomas Coscetta, 61, has shot “thousands of rounds” at trap-shooting competitions despite claiming a disability that caused “weakness in his extremities” and “shaking in his hands.”

* Retired conductor William McAleavey, 61, was charged with identity theft for allegedly using his son’s Social Security number to hide his employment as an ironworker. He had claimed that back injuries and carpal tunnel syndrome prevented him from lifting anything heavy.

The feds announced a final extension of the deadline for more than 1,500 other LIRR retirees to sign up for an amnesty program.

The new deadline is Sept. 28, with a second deadline of Oct. 26 that requires repaying half of what they swindled.